Electric machines such as, for example, electric generators are formed substantially from a movable part, the rotor, and an immovable part, the stator. The rotor comprises a rotor winding, which substantially comprises large-volume copper lines which are supplied current for generating a magnetic field via an excitation device. The rotating magnetic field induces a voltage in electrically conductive stator windings arranged in a suitable manner on the stator. Generally, such electric generators are embodied in such a way that the electrical lines form a stator end winding at the ends of the stator winding.
During operation of an electric machine, various physical effects result in loading of the individual component parts. Thus, energy is firstly dissipated by an electrical resistance both in the stator winding and in the rotor winding, and this energy results in thermal loading of the individual component parts. Furthermore, the rotors are generally operated at comparatively high speeds such as, for example, 50 or 60 Hz, which results in enormous centrifugal forces and in mechanical loading. Such high speeds result not only in relatively high levels of loading in the rotor, but also in the stator, in particular in the stator end winding. The vibrations or oscillations associated with the rotation can shorten the life of electric generators with such a design.
Electric generators are generally cooled by air, hydrogen or water, depending on the electric power requirement. The cooling medium is guided in substantially hermetically sealed fashion in a housing in the electric generator, so that the housing is substantially gas-tight with respect to the surrounding environment.
In general, the generators are designed for continuous operation and are correspondingly used to capacity. During inspection work which is performed when the electric generator is at a standstill, the stator end windings are visually inspected by an inspector. For this purpose, access through an opening, for example through so-called manhole covers, is enabled, as a result of which a visual inspection is possible. Nevertheless, such spatial conditions are constricted in such a way that access to the stator end windings is only possible by partially dismantling further generator components, such as, for example, the end plate upper parts.
A further problem arises in that, in particular in the case of generators cooled by hydrogen, the cooling medium (hydrogen) needs to be flushed out of the interior of the electric generator, which involves considerable complexity. Even after supposedly successful blowout and flushing of the electric machine with inert gas, the electric machine still needs to be made safe before it can be inspected by formaldehyde and oxygen concentration measurements being performed.
It would be desirable to have an inspection possibility which means a lower level of complexity in comparison with the prior art.